By Imogen Foulkes BBC News, Geneva

The last smallpox case was in 1977

Members of the World Health Organization (WHO) meeting in Geneva have approved recommendations for further research on the smallpox virus.

Health officials say it is necessary in order to develop new and better vaccines and anti-viral treatments.

Smallpox, which once killed millions, was eradicated worldwide in the late 1970s but stocks of the virus remain in laboratories in the US and Russia.

The WHO initially planned to destroy those stocks almost a decade ago.

'Biological weapon'

Since 1998, the WHO has been steadily moving away from its promise to destroy all stocks of smallpox.

The fear that the virus could get into the wrong hands and be used as a biological weapon has led many scientists to call for further research in order to develop new vaccines and anti-virals.

Rather than expanding the possibility of the re-introduction of smallpox into the world, we should be reducing the possibility Edward Hammond Sunshine Organization

The WHO's Dr Mike Ryan believes the organisation would be failing in its responsibility if it did not keep treatments up to date.

"We need to be absolutely sure that we have the necessary anti-virals and the necessary vaccines that we need to fight this virus, should someone release this from another source," he said.

WHO members, reflecting fears of a release, also called for strict controls of all new research.

Laboratories will only get parts of the virus to work on, not the whole thing, but the genetic sequence of smallpox is well known.

Opponents of research say continuing to experiment only increases the risk that someone will be able to recreate the virus and use it as a weapon of terror.

Edward Hammond, director of the Sunshine Organization, a group dedicated to bio-safety, said: "Rather than expanding the possibility of the re-introduction of smallpox into the world, we should be reducing the possibility, and the best way to do that is to destroy the smallpox stocks."